An application of panel loudspeakers in place of conventional loudspeakers has been known as means for outputting air conduction sound vibrating air when a mobile phone terminal receives a call or reproduces music (see PTL 1, for example). However, there may be a problem that it is difficult to hear the sound only with air conduction sound, when noises are larger than the air conduction sound.
By contrast, it is known that bone conduction is effective where ambient noises are large (see PTL 2, for example). However, strong vibration as produced in bone conduction that vibrates bones of the skull is not suitable for devices such as mobile phones that use little electricity in terms of power consumption. As the sound by bone conduction is small in the first place, it may be easily lost among the air conduction sound. Therefore, there is a drawback that a manufacturing process becomes complicated as it is necessary to increase the vibration, and a vibration unit and a casing are required to be configured separately so that the large vibration may not be conducted to the casing.
Further, in the conventional transducer, if a protecting panel is made of a hard material such as glass, or if the edges are adhered for waterproof, a large amount of electricity is required in order to vibrate a surface of the protecting panel. Therefore, the conventional transducer is not suitable for devices such as mobile phones that use little electricity in terms of power consumption.